赣东北蛇绿混杂岩带中大洋斜长花岗岩的地球化学和岩石成因

Geochemistry and petrogenesis of oceanic plagiogranitein the ophiolite from Northeast Jiangxi Province

赣东北蛇绿混杂岩带中的西湾斜长花岗岩富Ａｌ２ Ｏ３ 和Ｎａ２ Ｏ， 贫Ｋ２ Ｏ； Ｓｒ 、Ｂａ 和Ｔｈ 含量高， 而Ｒｂ 和高场强元素含量很低；ＬＲＥＥ 富集， 无Ｅｕ 异常；εＮｄ（ｔ） 值高， 为５．３９ 。（８７Ｓｒ／８６Ｓｒ）ｉ 低， 为０ ．７０２ ７ 。这些特征表明西湾斜长花岗岩是大洋斜长花岗岩。在Ｌａ／ＳｍＬａ 图中， 该斜长花岗岩与超基性岩和基性岩的分离结晶趋势不一致， 所以它不是岩浆分离结晶的产物，而可能是基性岩石小比例部分熔融的结果。

Xiwan oceanic plagiogranite occurs in NE Jiangxi ophiolite. It is characterized by high Al2O3 and Na2O and low K2O contents, higher Sr, Ba and Th, lower Rb and HFSE relative to continental plagiogranite. It is enriched in LREE, and without Eu anomaly. Nd and Sr isotopic compositions of the plagiogranite are characterized by high εNd(t) (5.39) and low (87Sr/86Sr)i (0.702 7). These characteristics show that Xiwan plagiogranite is oceanic plagiogranite. The plagiogranite is discordance with the evolution trend of ultra basic and basic rocks in La/Sm La diagram, which hints that it might not be the produce of magma fractional crystallization. It is most probably that the plagiogranite was derived from partial melting of basic rocks with small proportion.